The present invention generally relates to vehicle brakes and more particularly relates to an electromechanically actuated partially lined disk brake that can be used both for regular braking functions and parking brake functions.
This kind of electromechanically actuated disk brake is known from EP 0 728 089 B1. The disk brake described therein has a floating brake caliper as well as an actuating unit arranged on the brake caliper. The actuating unit exhibits an electric motor which sets an actuating element by means of an interposed reduction gear. The actuating element causes one of two brake linings displaceably arranged in the brake caliper to come into contact with a brake disk. The second brake lining also is pressed onto the brake disk by a reaction force acting on the brake caliper. Despite its compact structural design, this disk brake has a drawback in that it can only develop a limited braking force in both driving and parking brake functions.
DE 197 32 168 C1 describes a hydraulic vehicle brake with parking brake device, where a brake piston is arranged displaceably within a hydraulic chamber of the vehicle brake. The brake piston can be shifted into an actuating position within the brake caliper by means of hydraulic pressure: it acts together with a brake lining in such a way that the brake piston presses the brake lining against a brake disk. In order to ensure that, in addition to its function as a hydraulic driving brake, the vehicle brake also can be used as a parking brake, a spindle-and-nut configuration, which is driven by an electric motor, is arranged co-axially to the axis of the brake piston. Furthermore, a complex reduction gear is required in addition to an electric motor to generate the necessary clamping forces for a parking brake function. Thus, the above-mentioned vehicle brake needs two independent actuating paths, namely an hydraulic and an electromechanical one. This in turn requires a complex overall design of the vehicle brake and a complicated process for operating or controlling the vehicle brake.
The object of the present invention is to provide an electromechanically actuated partially lined disk brake that has a simple design and can be used both as a driving and parking brake and can be operated with economic efficiency and comfortably.
This object is solved by means of an electromechanically actuated partially lined disk brake of the present invention. Accordingly, the partially lined disk brake of the present invention comprises a brake caliper with an electromechanical actuating unit having at least two brake linings displaceably arranged in the brake caliper, each of which acts on a friction surface of a brake disk and one of which is brought into contact with the brake disk by means of at least one actuating element. In terms of effect a multi-step reduction gear is arranged between the actuating unit and actuating element, with the actuating unit, reduction gear and actuating element being located in a recess of the brake caliper that is configured as a housing. This allows a particularly compact design of the brake caliper, with the brake caliper being able to realize both the driving and parking brake functions. All in all, the multi-step reduction gear is configured as a non-self-locking device, i.e. it exhibits an overall efficiency of xcex7 greater than 50%. Thus, the clamping force from the electromechanical actuating unit to the brake linings is transmitted with as little loss as possible and, consequently, very efficiently. In addition, an engageable freewheel acting together with the reduction gear is included. By means of this engageable freewheel it is possible, in the event of activation, to lock the clamped brake caliper like a return stop in order to realize the parking brake function. In the direction of rotation of clamping of the actuating unit or non-self-locking reduction gear, the transmission of the brake clamping force from the actuating unit to the brake linings is not affected.
A particularly advantageous embodiment of the partially lined disk brake is achieved by having the reduction gear comprise a rolling-element ramp-type gear. This type of gear allows a rotary input variable to be converted into a translational output variable while ensuring a high reduction ratio. For this purpose, the rolling-element ramp-type gear preferably exhibits several ramps concentrically residing one inside others, allowing a large usable angle of torsion. The translational stroke of this type of gear is coordinated with the respective actuating stroke of the brake piston, in particular the translational stroke corresponds to this actuating stroke. For this purpose, the rolling-element ramp-type gear preferably comprises two ramp halves that can be twisted relative to one another; of these, the first ramp half is connected to the electromechanical actuating unit at the output end and a second ramp half is operatively connected to the actuating element. When the partially lined disk brake is operated, the two ramp halves can be twisted against one another to generate the actuating stroke and to transmit this to at least one of the brake linings via the actuating element. Preferably, the second ramp half, i.e. the one that is operatively connected to the actuating element, is secured against twisting; however, it must be possible to shift it in the housing of the brake caliper by the size of the actuating stroke of the brake lining.
According to a preferred embodiment of the invention, the engageable freewheel is designed as a return lock that is effective in the direction opposite to the direction of rotation of clamping of the reduction gear. When the brake is clamped, this return lock does not affect the function of the reduction gear. The non-self-locking reduction gear is prevented from reversing only in a clamped state and when the freewheel is blocked. Hence, the brake can be locked in a clamped state and, thus, secured against release of the brake due to decreasing clamping force of the brake. In order to release the brake, the lock function of the freewheel can be deactivated by means of a switching function when the reduction gear is rotated in the direction of release.
According to an advantageous embodiment of the invention, the multi-step reduction gear comprises a planetary gear step connected to the electromechanical actuating unit at the driving end as well as a spur gear step connected thereto, which acts together with the rolling-element ramp-type gear at the output end. By means of the planetary gear step in connection with the spur gear step, a particularly high step-down ratio is achieved for the entire reduction gear despite very low space requirements.
A particularly effective and easy-to-realize embodiment of the partially lined disk brake according to the present invention is achieved by providing the actuating element with a brake piston that is displaceably arranged in the brake caliper as well as at least one brake piston operatively connected to a brake lining, which is connected to the rolling-element ramp-type gear at the output end. As regards the overall design of the brake caliper in this connection, well-known design features of a brake caliper with a hydraulic actuating unit may be applied.
In order to maintain constant the translational stroke of the reduction gear when operating the partially lined disk brake, the actuating element preferably comprises also an adjusting device that is displaceably arranged in the brake caliper and can be extended in the clamping direction of the partially lined disk brake, wherein such adjusting device is operatively connected to at least one brake lining on the one hand and to the rolling-element ramp-type gear at the output end on the other hand. The extendable adjusting device takes into account the wear of the brake linings and is extended in proportion to the wear of the brake linings. Each actuating stroke of the brake piston or the stroke of the ramp half of the rolling-element ramp-type gear arranged displaceably in the direction of clamping in the brake caliper housing is maintained over the entire service life of the brake. In an advantageous design, the adjusting device includes a nut-and-spindle configuration which acts together on the one hand with the brake piston and on the other hand with the rolling-element ramp-type gear. Nut and spindle are connected by a thread in such a way that they can be twisted in relation to one another, with the spindle being connected in a twist-proof manner to the second ramp half arranged displaceably in the brake caliper housing.
According to another advantageous embodiment of the invention, the partially lined disk brake exhibits a hydraulic actuating device that is independent of the electromechanical actuating unit. In particular, this hydraulic actuating device is formed by a cylinder bore in the brake caliper in connection with the brake piston. Within such a configuration the hydraulic actuating device can be used for driving brake operations and the electromechanical actuating unit for parking brake operations. Thus, the two different modes of actuation can be designed and configured specifically for their respective function.
A particularly low-cost partially lined disk brake according to the present invention is achieved when the electromechanical actuating unit is formed by a direct current (DC) electric motor. Such electric motors are known in many different designs and can be used within the brake as a standardized component.
In a preferred embodiment of the partially lined disk brake, the electric motor has an angular-position sensor that is connected to the rotary movement of the electric motor, in particular can be integrated in the reduction gear or electric motor. Thus the current motor position and motor movement with direction of rotation and speed can be detected at any time and, consequently, provides information on the corresponding actuating state of the partially lined disk brake.
According to a further embodiment of the invention, the reduction gear is provided with a tool holding fixture to attach an emergency actuating element. In this way, an emergency actuation of the brake, i.e. releasing or clamping, is possible in the event of a malfunction, e.g. when there is no sufficient electric power supply.
An advantageous embodiment of the invention is achieved when at least the electromechanical actuating unit, planetary gear as well as a driving wheel of the spur gear form a first independent subassembly, which is arranged and fixed in the recess of the brake caliper that is configured as a housing. Furthermore, this first subassembly can be supplemented by additional meaningful single parts. Hence, this module can be preassembled simply outside the brake caliper and, after being inserted in the recess of the brake caliper, it can, for example, be fastened with screws. In the same way, it would be meaningful for at least the rolling-element ramp-type gear, engageable freewheel as well as an output wheel of the spur gear to form another independent subassembly. This second subassembly also can be preassembled and, finally, fastened in the recess of the brake caliper that is configured as a housing. These subassemblies give rise to a particularly easy-to-assemble modular design of the partially lined disk brake.
According to a preferable embodiment of the invention, the electromechanical actuating unit, actuating element as well as multi-step reduction gear are arranged and fastened within the brake caliper and sealed off against their surroundings by means of a housing cover. Thus, a particularly compact design is achieved for the brake caliper and, also, the individual assemblies of the partially lined disk brake can be accessed quickly and in an easy-to-assemble manner simply by removing the housing cover. The housing cover prevents contamination of the individual subassemblies and, hence, ensures safe operation of the brake.